Carbon composite materials comprising particles of metal carbides dispersed therein and method for producing the same

ABSTRACT

This invention provides carbon composite materials, which comprise metal carbide particles, at least the particle surfaces or the entirety of which are metal carbides, synthesized in situ from a metal source, i.e., at least one member selected from the group comprising metal particles, metal oxide particles, and composite metal oxide particles, and a carbon source, i.e., a thermosetting resin, dispersed in a carbon, carbon fiber, or carbon/carbon fiber matrix, and contain no free metal particles. This invention also provides a method for producing such composite carbon materials, which enables the production of carbon composite materials having a high coefficient of friction, high thermostability, and abrasion resistance.

TECHNICAL FIELD

The present invention relates to carbon composite materials having ahigh coefficient of friction, high thermostability, and abrasionresistance. Also, the present invention relates to a method forproducing such carbon composite materials.

BACKGROUND ART

Carbon materials are combined with carbon fibers to prepare compositematerials. Such process is known to be effective in order to improve theperformance of such materials. For example, carbon fiber/carboncomposite materials comprising high-strength carbon fibers are known asCC composite materials. Such materials are superior in specific strength(i.e., strength/density) to conventional metal materials, and thus, theapplications of such composite materials are being expanded in variousfields. For example, such CC composite materials are used for brake padmaterials of automobiles or aircraft.

A variety of techniques for preparing reinforced carbon compositematerials have been attempted via dispersion of second-phase particlesin carbon materials. While the addition of dispersed particles resultsin the improved abrasion resistance of composite materials, the addedparticles sometimes become fracture origins in the materials anddisadvantageously deteriorate the strength of the materials. In order toimprove both the strength and the abrasion resistance of carbonmaterials via incorporation of second-phase particles, accordingly, itis necessary that fine second-phase particles be added in an amountrequired so as to result in a lack of deterioration of the strength ofthe material. It is necessary to add fine second-phase particles havingan average particle diameter of 1 μm or smaller in order to realizesatisfactory strength. It is deduced that the second-phase particleswith the carbon matrix phase are suitable. Examples of such particlesinclude high-purity metal carbides, such as tungsten carbide, titaniumcarbide, and silicon carbide, which remain stable without denaturingduring the process of producing given members.

Production of fine particles of high-purity metal carbides in acost-effective manner, however, involves serious technical difficulties.As the diameters of particles of metal carbides become small, dispersionof particles in a material with a carbon matrix phase becomes difficultdue to aggregation or other activities. Accordingly, it is technicallydifficult to homogeneously incorporate such particles in a material witha carbon matrix phase. During the process for producing fine particleswith very large specific surface areas, the surfaces of such particlesare easily oxidized. Thus, it is practically impossible to preparecomposite materials composed of carbon materials and fine particles ofhigh-purity metal carbides.

JP Patent Publication (Kokai) No. 11-130537A (1999) discloses a methodfor producing a carbon composite material comprising particles ofreinforcing metal carbides each with an average particle diameter of 1μm or smaller dispersed therein, wherein starting powder materialshaving carbon matrix phases are mixed with at least one kind of metaloxide in advance, the mixture is molded and then calcined, and thecalcination product is impregnated with pitch, followed byrecalcination. This method is intended to produce carbon compositematerials comprising particles of reinforcing, high-purity, and finemetal carbides dispersed therein in efficient and cost-effectivemanners.

JP Patent Publication (Kokai) No. 11-217267A (1999) discloses a methodfor producing two-dimensional fiber-reinforced silicon carbide-carboncomposite ceramics comprising forming a formed product comprisingsilicon powder, a resin as a carbon source, and a two-dimensionalfiber-reinforced material into a desired shape, carbonizing the formedproduct at 900° C. to 1,300° C. in an inert gas atmosphere, impregnatingthe resultant with a resin, re-sintering the impregnated material at900° C. to 1,300° C. in an inert gas atmosphere, iterating the resinimpregnation and sintering, and finally sintering the material at about1,350° C. to 1,500° C. in an inert gas atmosphere. This method isintended to readily produce two-dimensional fiber-reinforced siliconcarbide-carbon composite ceramics having high strength and complicatedshape regardless of high open porosity via impregnation of the ceramicswith a resin and the reaction sintering method.

SUMMARY OF THE INVENTION

According to the method disclosed in JP Patent Publication (Kokai) No.11-130537A (1999), powdery metal oxides are mixed with powdery carbon,and the dispersibility of the generated metal oxides is not sufficient.Thus, the amount of carbon provided in the vicinity of metal oxides wasnot sufficient, and the reaction between metal oxides and carbon was notsufficiently carried out.

According to the method disclosed in JP Patent Publication (Kokai) No.11-217267A (1999), SiC is generated by a direct reaction between siliconmetal and carbon. Accordingly, unreacted silicon metalsdisadvantageously remained as free silicon metals.

It is an object of the present invention to provide carbon compositematerials having a high coefficient of friction, high thermostability,and abrasion resistance, and to provide a method for producing suchcarbon composite materials.

The present inventors discovered that such object could be attained bycombining a given metal source with a carbon source and generatingparticles of metal carbides in situ. This has led to the completion ofthe present invention.

Specifically, the first aspect of the present invention concerns carboncomposite materials, which comprise metal carbide particles, at leastthe particle surfaces or the entirety of which are metal carbides,synthesized in situ from a metal source, i.e., at least one memberselected from the group comprising metal particles, metal oxideparticles, and composite metal oxide particles, and a carbon source,i.e., a thermosetting resin, dispersed in a carbon, carbon fiber, orcarbon/carbon fiber matrix, and contain no free metal particles.

The average particle diameter of the metal carbide particles, metaloxides, or composite metal oxides synthesized in situ in the carboncomposite materials is not particularly limited. For example, it may be2 μm to 5 μm. The shape of the metal carbide particles, metal oxides, orcomposite metal oxides is not particularly limited. For example, suchparticles may be approximately spherical or nonspherical in shape.

Preferably, a metal source is at least one member selected from thegroup comprising metal particles of Si, Ti, Zr, Al, W, Cr, and Zn, forexample. These metal particles may be oxidized to obtain SiO₂, TiO₂,ZrO₂, Al₂O₃, WO₃, CrO₃, or ZnO particles, and at least one type of metaloxide particles or composite metal oxide particles selected therefrom isalso preferably used as a metal source.

More specifically, it is preferable that the particles of metal oxidesas a metal source be SiO₂ particles, and that the metal carbideparticles generated therefrom be SiC particles. Preferable examples ofSiO₂ particles include spherical silica particles obtained by a reactionbetween silicon metal and oxygen, spherical silica particles obtained bymelting fragmented silica, and fragmented silica particles. Also, it ispreferable that the particles of composite metal oxides as a metalsource be particles of SiO₂/ZrO₂ composite metal oxides and the metalcarbide particles generated therefrom be the particles of SiC/ZrCcomposite carbides.

The second aspect of the present invention concerns a method forproducing carbon composite materials comprising metal carbide particlesdispersed therein, wherein at least one of metal particles, metal oxideparticles, or composite metal oxide particles is dispersed in athermosetting resin to obtain a slurry mixture, carbon fibers areimpregnated with the slurry mixture, and carbonation is carried out tosynthesize metal carbides in situ, at least the particle surfaces or theentirety of which are metal carbides, followed by calcination.

FIG. 1 shows a flow chart showing an example of a process for producingcarbon composite materials comprising metal carbide particles dispersedtherein.

As in the case of the first aspect of the present invention, at leastone metal source selected from the group comprising metal particles ofSi, Ti, Zr, Al, W, Cr, or Zn is preferably used, for example. Also,these metal particles may be oxidized to obtain SiO₂, TiO₂, ZrO₂, Al₂O₃,WO₃, CrO₃, or ZnO particles, and at least one type of metal oxideparticles or composite metal oxide particles selected therefrom is alsopreferably used as a metal source.

More specifically, it is preferable that the particles of metal oxidesas a metal source be SiO₂ particles and that the metal carbide particlesgenerated therefrom be SiC particles. Preferable examples of SiO₂particles include spherical silica particles obtained by a reactionbetween silicon metal and oxygen, spherical silica particles obtained bymelting fragmented silica, and fragmented silica particles.

A thermosetting resin as a carbon source is not particularly limited.For example, a thermosetting resin, such as phenol resin, melamineresin, urea resin, epoxy resin, unsaturated polyester resin, alkydresin, silicone resin, diallyl phthalate resin, polyamide-bismaleimideresin, or polybisamide triazole resin, or a thermosetting resin composedof two or more of such resins, can be used. A phenol resin with highcarbon content is particularly preferable.

In the present invention, a method for producing a slurry mixturecomprising at least one metal source selected from the group comprisingmetal particles, metal oxide particles, and composite metal oxideparticles dispersed in a thermosetting resin as a carbon source is notparticularly limited. In order to obtain a stable slurry mixture withgood dispersion conditions, a dispersion stabilizer is preferably addedto the slurry mixture, or particles as a metal source are preferablytreated with a surfactant.

Since the slurry mixture is a solution comprising metal oxide particlesand a dispersant incorporated in a phenol resin solution, use of adispersant enables homogeneous dispersion of metal oxides in phenolresin. Homogeneous dispersion of metal oxides allows carbon to bepresent in an amount required for the reaction, which in turn realizeseffective reactions.

In the present invention, a step of thermocompression bonding is carriedout by laminating the impregnation product, following the step ofimpregnation and prior to the step of carbonization. Thus, carboncomposite materials with a given thickness and strength can be obtained.

In the present invention, it is preferable to carry out the step ofimpregnating the carbon fiber materials with the slurry mixturecomprising particles as a metal source dispersed in a thermosettingresin as a carbon source two or more times from the viewpoint of theproduction of high-density metal carbides. For example, prior to in situproduction of metal carbide particles by the process of calcination,particles as a metal source are dispersed in a thermosetting resin toobtain a slurry mixture, and carbon fibers are impregnated with theslurry mixture for carbonization. This procedure is carried out two ormore times. Alternatively, following in situ production of metal carbideparticles by the process of calcination, particles as a metal source aredispersed in a thermosetting resin to obtain a slurry mixture, andcarbon fibers are impregnated with the slurry mixture for carbonization.This procedure is iterated one or more times.

A reaction whereby silicon carbide is generated by allowing silica toreact with carbon in the process of calcination is a solid-gas reaction.Since silicon monoxide reacts with carbon in the gas phase, importanceis given to complete coverage of silica particles with carbon withoutleaving any gaps, in order to prepare particulate silicon carbides.After molding of the composite material, the phenol resin is carbonizedby heating at 500° C. or higher, and contracted. Thus, gaps are formed.Silicon monoxide gas leaks from such gaps, and particulate siliconcarbides are less likely to be formed. Prior to the step of calcination,the molding product is reimpregnated with liquid phenol resin,carbonization is then carried out, and silica particles are completelycovered with carbon without leaving any gaps. Thus, particulate siliconcarbides are generated.

In the present invention, carbonization is carried out at 200° C. to1600° C., and preferably at 500° C. to 1000° C., in an inert gasatmosphere. Calcination is carried out at a temperature at which athermosetting resin is thermally decomposed in an inert gas atmosphereand becomes a carbon source, such as at 1650° C. or higher.

The third aspect of the present invention concerns friction materialscomprising the aforementioned carbon composite materials. With theutilization of properties of carbon composite materials, such as a highcoefficient of friction, high thermostability, and abrasion resistance,such friction materials can be put to a variety of applications.Particularly effective applications of such materials are, for example,brake rotor and/or pad materials of automobiles or aircraft.

The carbon composite materials according to the present invention haveproperties such as a high coefficient of friction, high thermostability,abrasion resistance, and lightness in weight.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a flow chart showing a process for producing carboncomposite materials of the present invention.

FIG. 2 shows a secondary electron image of a test piece molded accordingto the present invention.

FIG. 3 shows a secondary electron image of silicon carbide, which wassubjected to molding, carbonization, and then calcination immediatelythereafter.

FIG. 4 shows the configuration of particles in a treated test piece thatwas subjected to molding, carbonization, reimpregnation with phenolresin, recarbonization, and then calcination.

FIG. 5 shows a photograph of a TEM image of a sample comprising SiCsynthesized in situ.

FIG. 6 shows a photograph of a TEM image of a sample comprising SiCmixed therewith.

FIG. 7 shows a photograph of a TEM image of a sample comprising SiCsynthesized in situ, which is the same as that of FIG. 5.

FIG. 8 shows the results of EDX qualitative analysis at sites A and Bshown in FIG. 7.

FIG. 9 shows the results of EDX qualitative analysis at sites C and Dshown in FIG. 7.

FIG. 10 shows a photograph of a TEM image of a sample comprising SiCmixed therewith, which is the same as that of FIG. 6.

FIG. 11 shows the results of EDX qualitative analysis at sites A to Cshown in FIG. 10.

PREFERRED EMBODIMENTS OF THE INVENTION

Hereafter, the present invention is described with reference to anexample of a carbon composite material comprising silicon oxide (silica:SiO₂) as a metal source.

A conventional technique is based on a direct reaction of metal (Si) andcarbon (C). In the present invention, however, gas-phase SiO isgenerated by the stepwise reactions (1) and (2) shown below, and the SiOgas then reacts with carbon (C) to generate SiC.SiO₂+C→SiO↑+CO↑  (1)SiO+2C→SiC+CO↑  (2)Such a reaction whereby silica is allowed to react with carbon togenerate silicon carbide is a solid-gas reaction, and complete coverageof silica particles with carbon without leaving any gaps is critical inorder to generate particulate silicon carbide.

The reaction represented by formula (1) is carried out in combinationwith the reaction represented by formula (2) to realize the reactionrepresented by formula (3).SiO₂+3C→SiC+2CO↑  (3)Thus, metal carbide SiC is generated in situ with the use of metal oxide(SiO₂).

Advantageously, such reaction does not involve a free metal, and no freemetal is present. Thus, a high coefficient of friction and highthermostability are exhibited. By regulating the amount and theconfiguration of SiO₂, the amount, the configuration, the particlediameter, and the like of SiC generated can be freely regulated. Withthe use of spherical SiO₂ sold by Admatechs Co., Ltd., spherical SiC canbe synthesized in situ in carbon-carbon fiber composites (CCcomposites).

The present invention involves the use of a homodisperse slurry systemcomprising SiO₂ particles monodispersed in a solution of thermosettingresin precursors, such as a phenol resin, without aggregation. Thus, thesurfaces of SiO₂ particles generated from the thermosetting resinprecursors are covered via coating. This can prevent a reaction betweena reinforcing material, i.e., carbon fiber, and SiO₂. Thus, the strengthof the materials would not become deteriorated due to damaged carbonfibers, and the composite materials of the present invention aresuperior in strength to conventional composite materials.

More specifically, the features of the present invention are summarizedas follows.

(1) Use of stable slurry comprising SiO₂ particles monodispersed in asolution of thermosetting resin precursors.

(2) Use of thermosetting resin precursors, SiO₂, and carbon fibers asstarting materials.

(3) Performance of in situ reaction of SiO₂ selectively with carbongenerated from thermosetting resin precursors to generate SiC andprevention of reaction of SiO₂ with carbon fibers.

(4) Firm conjugation of SiC with a carbon matrix phase via formation ofa diffusion reaction phase.

(5) Homogeneous dispersion of generated SiC particles.

(6) A SiC/carbon/carbon fiber composite containing no free Si particles.

Hereafter, the carbon composite of the present invention is describedusing an electron micrograph.

FIG. 2 shows a secondary electron image of a test piece molded accordingto the present invention. In FIG. 2, particulate substances are thegenerated metal carbides. In the process of allowing metal oxides toreact with carbon to generate metal carbides, it is important that asufficient amount of carbon be positioned in the vicinity of the metaloxide particles without metal oxide aggregation. According to aconventional technique, when metal oxides and carbon are both powders,aggregation of some metal oxides is inevitable. According to the presentinvention, however, homogeneous dispersion of metal oxides in carbon wasrealized via incorporation of particles of metal oxides and a dispersantin a phenol resin solution.

A reaction whereby silica particles are allowed to react with carbon togenerate silicon carbides is a solid-gas reaction. In order to generateparticulate silicon carbides, the peripheries of the silica particlesmust be completely covered with carbon without leaving any gaps. FIG. 3shows a secondary electron image of silicon carbide, which was preparedby dispersing metal oxide particles in a phenol resin solution andsubjected to molding and carbonization, followed by calcinationimmediately thereafter. Via a single operation of impregnation with aphenol resin solution and carbonization, silicon carbides generated hadparticle diameters of 1 μm or smaller.

FIG. 4 shows the configuration of particles in the treated test piece,which was prepared by subjecting a solution similar to that of FIG. 3 tomolding, carbonization, reimpregnation with a phenol resin,recarbonization to provide a sufficient amount of carbon around thesilica particles, and then calcination. As is apparent from FIG. 4,spherical silicon carbide particles with diameters of 2 μm to 5 μm aregenerated by subjecting the test piece to impregnation with phenol resinand carbonization twice, prior to calcination.

Metal oxides used in the present invention may be selected in accordancewith, for example, reactivity with carbon materials or applications ofcarbon composite materials, without particular limitation. Examples ofmetal oxides include titanium oxide, chromium oxide, tungsten oxide,niobium oxide, silicon oxide, zirconium oxide, hafnium oxide, tantalumoxide, molybdenum oxide, and vanadium oxide.

Metal oxide particles or composite metal oxide particles that areobtained by oxidizing metal powders can be used. For example, any ofsilica, alumina, zirconia, mullite, spinel, and zinc oxide can bepreferably used. Particularly preferably, spherical silica particlesobtained by a reaction of silicon metal with oxygen, spherical silicaparticles obtained by melting fragmented silica, silica particlesselected from among fragmented silica products, spherical aluminaparticles obtained by a reaction of aluminum metal with oxygen,spherical alumina particles obtained by melting fragmented alumina, andalumina particles selected among fragmented alumina products are used.

Metal oxide particles obtained by sintering metals are prepared in thefollowing manner. That is, a chemical flame is formed in an atmospherecontaining a carrier gas and oxygen, metal powder mixtures, such aspowders of metals such as silicon, aluminum, magnesium, zirconium, ortitanium, aluminum and silicon powders blended in mullite compositions,magnesium and aluminum powders blended in spinel compositions, andaluminum, magnesium, or silicon powders blended in cordieritecompositions, are introduced into the chemical flame, and fine particlesof metal oxides or composite metal oxides of interest, such as silica(SiO₂), alumina (Al₂O₃), titania (TiO₂), or zirconia (ZrO₂), are thenproduced in the chemical flame. Such particles of metal oxides aremanufactured and sold by Admatechs Co., Ltd.

EXAMPLES

Starting materials of 1) silica particles with an average particlediameter of 3 μm and 2) liquid phenol resin were used. Silica particleswere introduced into liquid phenol resin with a dispersant to adjusttheir concentrations to a C:Si ratio of at least 3:1, in terms of molarratio. In this example, silica particles were mixed at a ratio of C:Siof 9:1, in terms of molar ratio.

A carbon sheet was impregnated with the aforementioned slurry, followedby molding via heating. After molding, the dispersion state of silicaparticles was observed under an electron microscope, and the photographshown in FIG. 2 was obtained.

The molding product was subjected to carbonization in an inert gasatmosphere at 1000° C.

The carbon sheet was reimpregnated with phenol resin in a vacuumcontainer, followed by recarbonization. Thereafter, the molding productwas subjected to calcination in an inert gas atmosphere at 1650° C. Theresulting test piece was observed under an electron microscope in orderto inspect the particle shape. The test piece was simultaneouslysubjected to X-ray diffraction analysis and it was confirmed to besilicon carbide. FIG. 4 shows an electron micrograph.

[Comparison of in situ Synthesis of SiC and Simple Incorporation of SiC]

In the present invention, SiC particles contained in carbon compositematerials are synthesized upon in situ reaction between silica particlesand carbon at the time of calcination. The interface of SiC generated insitu and carbon was compared with the SiC/C/C composite materialprepared via simple mixing of SiC to evaluate the effects of the in situreaction.

[Comparison of TEM Images]

The sample comprising SiC generated via in situ reaction was obtained bymixing spherical silica particles (average particle diameter: 3 μm) withphenol resin, curing the mixture to prevent foaming, and then calcifyingthe cured product at 1750° C. for 2 hours. The sample comprising SiC viasimple mixing was obtained by mixing SiC particles (particle diameter: 2to 3 μm) with phenol resin, curing the mixture to prevent foaming, andthen calcifying the cured product at 1750° C. for 2 hours.

The SiC/carbon interfaces of these two samples were observed by TEM.FIG. 5 shows a photograph of a TEM image of a sample comprising SiCsynthesized in situ. FIG. 6 shows a photograph of a TEM image of asample comprising SiC mixed therewith. At the SiC/carbon interface, anintermediate layer is generated and no gaps are observed in thephotograph shown in FIG. 5, although some gaps are observed in thephotograph shown in FIG. 6. This indicates that adhesion between SiC andcarbon becomes improved via generation of SiC by in situ reaction.

[Comparison of EDX Qualitative Analysis]

The TEM image of a sample comprising SiC synthesized in situ shown inFIG. 5 is shown again in FIG. 7. FIGS. 8 and 9 show the results of EDXqualitative analysis at sites A to D shown in FIG. 7. As is apparentfrom the results, site A represents SiC generated and site D representscarbon. As shown in the figures showing the results of EDX qualitativeanalysis, the Si peak intensity becomes smaller as the site forobservation gets closer to site D from site A, and sites B and C areintermediate layers resulting from in situ reactions. Also, there are nogaps at the SiC/carbon interface, and SiC particles adhere to carbon.

The TEM image of a sample comprising SiC mixed therewith shown in FIG. 6is shown again in FIG. 10. FIG. 11 shows the results of EDX qualitativeanalysis at sites A to C shown in FIG. 10. As is apparent from theresults, site A represents carbon and sites B and C each represent SiC,which was mixed in the sample. There are gaps at the SiC/carboninterface, and SiC particles do not adhere to carbon.

There were no gaps at the interface of SiC generated in situ and carbon,but there were gaps at the interface of SiC, which was mixed in thesample, and carbon. This indicates that generation of SiC via in situreaction can realize better adhesion between SiC particles and carbon.

INDUSTRIAL APPLICABILITY

The carbon composite materials of the present invention have propertiessuch as a high coefficient of friction, high thermostability, abrasionresistance, and lightness in weight. Thus, such materials can be usedfor a variety of applications as friction materials with the utilizationof such properties. Also, such carbon composite materials have lowproduction costs and thus are practical.

1-18. (canceled)
 19. Friction materials, which comprise metal carbideparticles, at least the particle surfaces or the entirety of which aremetal carbides, synthesized in situ from a metal source, i.e., at leastone member selected from the group comprising metal particles, metaloxide particles, and composite metal oxide particles, and a carbonsource, i.e., a thermosetting resin, dispersed in a carbon, carbonfiber, or carbon/carbon fiber matrix, and contain no free metalparticles.
 20. The friction materials according to claim 19, wherein themetal oxide particles or composite metal oxide particle are at least onetype of metal selected from the group comprising SiO₂, TiO₂, ZrO₂,Al₂O₃, WO₃, CrO₃, or ZnO particles obtained by oxidizing metal powders.21. The friction materials according to claim 20, wherein the metaloxide particles are SiO₂ particles and the metal carbide particles areSiC particles.
 22. The friction materials according to claim 20, whereinthe composite metal oxide particles are SiO₂/ZrO₂ composite metal oxideparticles and the metal carbide particles are SiC/ZrC composite carbideparticles.
 23. The friction materials according to claim 21, wherein theSiO₂ particles are selected from among spherical silica particlesobtained by a reaction between silicon metal and oxygen, sphericalsilica particles obtained by melting fragmented silica, and fragmentedsilica particles.
 24. A method for producing friction materialscomprising metal carbide particles dispersed therein, wherein at leastone of metal particles, metal oxide particles, or composite metal oxideparticles is dispersed in a thermosetting resin to obtain a slurrymixture, carbon fibers are impregnated with the slurry mixture, andcarbonization and calcination are carried out to carbonize thethermosetting resin to generate metal carbides in situ, at least theparticle surfaces or the entirety of the particles of which are metalcarbides.
 25. The method for producing friction materials according toclaim 24, wherein the metal oxide particles or composite metal oxideparticles are at least one member selected from the group comprisingSiO₂, TiO₂, ZrO₂, Al₂O₃, WO₃, CrO₃, and ZnO particles obtained byoxidizing metal powders.
 26. The method for producing friction materialsaccording to claim 25, wherein the metal oxide particles are SiO₂particles and the metal carbide particles are SiC particles.
 27. Themethod for producing friction materials according to claim 25, whereinthe composite metal oxide particles are SiO₂/ZrO₂ composite metal oxideparticles and the metal carbide particles are SiC/ZrC composite carbideparticles.
 28. The method for producing friction materials according toclaim 26, wherein the SiO₂ particles are selected from among sphericalsilica particles obtained by a reaction between silicon metal andoxygen, spherical silica particles obtained by melting fragmentedsilica, and fragmented silica particles.
 29. The method for producingfriction materials according to claim 24, wherein the thermosettingresin is at least one member selected from the group comprising phenolresin, epoxy resin, unsaturated polyester resin, acrylic resin, urearesin, furan resin, diallyl phthalate resin, melamine resin,polyurethane resin, and aniline resin.
 30. The method for producingfriction materials according to claim 24, wherein a step ofthermocompression bonding is carried out by laminating the impregnationproduct, following the step of impregnation and prior to the step ofcarbonization.
 31. The method for producing friction materials accordingto claim 24, wherein, prior to in situ production of metal carbideparticles by the process of calcination, a step of impregnating thecarbon fiber materials with a slurry mixture comprising at least onetype of metal oxide particles dispersed in a thermosetting resin forcarbonization is carried out two or more times.
 32. The method forproducing friction materials according to claim 24, wherein, followingin situ production of metal carbide particles by the process ofcalcination, a step of impregnating the carbon fiber materials with aslurry mixture comprising at least one type of metal oxide particlesdispersed in a thermosetting resin for carbonization is iterated one ormore times.
 33. The method for producing friction materials according toclaim 24, wherein carbonization is carried out in an inert gasatmosphere at 200° C. to 1600° C.
 34. The method for producing frictionmaterials according to claim 24, wherein calcination is carried out inan inert gas atmosphere at 1650° C. or higher.
 35. The frictionmaterials according to claim 19, wherein the friction materials arebrake rotor and/or pad materials.